TUI: transcript-mode edit in /side conversation crashes with thread/rollback failed instead of graceful rejection

What version of Codex CLI is running?

@openai/codex@alpha = 0.140.0-alpha.11

What subscription do you have?

$100/mo

Which model were you using?

any

What platform is your computer?

Linux 6.12.90+deb13-amd64 x86_64 unknown

What terminal emulator and version are you using (if applicable)?

Any

Codex doctor report

irrelevant

What issue are you seeing?

In the TUI, editing previous prompts is correctly blocked in /side conversations through the normal edit/backtrack path with:

■ Editing previous prompts is unavailable in side conversations.

However, the same unsupported action can still be reached through transcript mode. When I enter transcript mode from a /side conversation and confirm the selected prior message, the TUI crashes and shows:

Error: thread/rollback failed in TUI

This is still broken on the latest alpha (0.140.0-alpha.11) as well as stable 0.139.0.

What steps can reproduce the bug?

1. Start a Codex TUI session.
2. Send a message in the main conversation.
3. Receive a response.
4. Start a side conversation with /btw or /side.
5. Send a message in the side conversation.
6. Receive a response.
7. Press Ctrl+T to enter transcript mode.
8. Press Esc to select the last message / enter backtrack selection.
9. Press Enter to attempt to edit that selected message.

What is the expected behavior?

The TUI should gracefully reject editing previous prompts in side conversations, matching the existing behavior from the normal edit/backtrack path:

■ Editing previous prompts is unavailable in side conversations.

The TUI should remain open and usable.

Actual behavior:

The TUI crashes and prints:

Error: thread/rollback failed in TUI

Additional information

_No response_